Prevention of enteric bacterial infections and modulation of gut microbiota composition with conjugated linoleic acids producingLactobacillusin mice

Probiotics are recognized to outcompete pathogenic bacteria by receptor-mediated colonizing and secreting functional metabolites which have direct antimicrobial activities towards pathogens and/or improving host’s gut health and immunity. We have constructed a Lactobacillus casei (LC) probiotic strain, LC + mcra , by inserting mcra (myosin cross-reactive antigen) gene, which stimulates the conversion of conjugated linoleic acids. In this study, we evaluated the protective roles of LC + mcra against pathogenic Salmonella enterica serovar Typhimurium (ST) and enterohaemorrhagic E. coli (EHEC) infection in BALB/cJ mice. Through a series of in vivo investigation, we observed that LC + mcra colonized efficiently in mice gut and competitively reduced the infection with ST and EHEC in various locations of small and large intestine, specifically cecum, jejunum, and ileum ( p <0.05). The cecal microbiota in ST-challenged mice with LC + mcra protection were positively modulated with higher relative abundances Firmicutes but lower Proteobacteria plus increased bacterial species diversity/richness based on 16S metagenomic sequencing. Based on cytokine gene expression analysis by qRT-PCR, mice pretreated with LC + mcra were found with attenuated bacterial pathogen-induced gut inflammation. Furthermore, mice fed LC + mcra daily for one week could protect themselves from the impairments caused by enteric infections with ST or EHEC. These impairments include weight loss, negative hematological changes, intestinal histological alterations, and potential death. This in vivo study suggests that daily consumption of novel conjugated linoleic acids over-producing probiotic might be efficient in improving gut intestinal microbiome composition and preventing/combating foodborne enteric bacterial infections with pathogenic Salmonella and diarrheagenic E. coli. Author summary Numerous bacteria colonize throughout the gastrointestinal tract and form a complex microbial ecosystem known as gut microbiota. A balanced microbial composition is crucial for maintaining proper gut health and host defense against pathogenic microbes. However, enteric bacterial infections could cause illness and even lead to death of host when foodborne pathogens like Salmonella and enterohaemorrhagic E. coli (EHEC) invade gut intestine and cause imbalance of gut microbiota. Beneficial microbes in gastrointestinal tract such as Lactobacillus and their secreted bio-active metabolites, are potential bio-agents to improve gut immunity and outcompete bacterial pathogens. In this study, to evaluate roles of novel Lactobacillus strain LC + mcra which produce higher amount of a group of beneficial secondary metabolites called conjugated linoleic acids, we have shown that daily oral administration of this LC + mcra for one-week in mice lead to higher proportion of beneficial bacterial colonization in different locations of intestine and a significant reduction of pathogenic Salmonella and EHEC colonization. Furthermore, mice fed with LC +mcra restore and modulate Salmonella infection-induced negative impact on gut microbiota composition and protect themselves from various levels of physiological damage.